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                                SWFARINGEN SX300
                                               Two seats and turboprop performance

      It is, in certain respects, the ultimate kit-built                                                     spar. The leading edge is stretch-formed,
      airplane. The fastest, with a top speed of 239                                                         meaning that it is stretched into shape by
      knots. The most expensive, at $43,021 for a                                                            pressing a mold into a sheet of aluminum.
      series of six construction kits (not including                                                         This technique enables the leading edge con-
      engine, propeller, avionics, instrumentation,                                                          tours to be formed with a high degree of con-
      upholstery and paint). And perhaps the most                                                            formity to design specifications.
      complex to build. For many pilots, the                                                                    Rear wing skins join the leading edge in a
      Swearingen SX300 may represent the ulti-                                                               joint that is recessed one tenth of an inch
      mate personal airplane available from any                                                              below the aerodynamic contour of the wing.
      source, whether it be a factory production                                                             This depression is filled in with a synthetic
      line or a kit-maker's packing crate.                                                                   compound that is flexible when dried and
         The SX300 is the invention of designer/                                                             will not crack, according to Swearingen.
      entrepeneur Edward J. Swearingen Jr., who is          Swearingen, the designer alld the design         Carefully applied and sanded before paint-
      best known for the line of aircraft that bears                                                         ing, the filler is almost unnoticeable, even un-
      his name-the Swearingen Merlin and Metro             knots, slowing to 80 over the threshold. Stall    der close inspection, and the wing takes on a
      turboprops. Swearingen sold the line to the          speed in the landing configuration is 70 knots    seamless look.
      Fairchild Aircraft Corporation 15 years ago,         at gross weight. With gear and flaps up, stall      The wing section is a natural laminar flow
      and updated versions of those aircraft now           speed rises to 75 knots.                          (NLF) design, an NLF(1)-0416, to be precise.
      are marketed as the Fairchild 300, 400 and              It might seem that combining a big engine      As the airfoil's designer, NASA engineer Dan
      Metro. Among other projects, Swearingen              with a small airframe would be a simple for-      M. Somers, explains it, NLF airfoils, designed
      also was involved in the development of the          mula for high performance. The trick, of          with the aid of computers, offer the low drag
      Twin Comanche, the Cheyenne and a proto-             course, is to make the airplane an efficient,     factors of earlier laminar-flow designs com-
      type for a pre-Malibu pressurized single             sturdy and stable machine. The engineering        bined with the high lift coefficients of turbu-
      while working under contract to Piper Air-           that has gone into the SX300 is more typical      lent-flow airfoils. Earlier laminar-flow de-
      craft in the 1960s and early 1970s.                  of the approach taken in designing a business     signs could not match the high lift produced
          For Swearingen, speed always has been a          jet than a general aviation single.               by non-laminar-flow airfoils. Because of the
      high design priority. The keys to superior              Wing and fuselage skins are heavy-gauge        high-lift properties of the SX300's wing sec-
      performance, in his view, are plenty of              .040-inch-thick aluminum alloy. The skins         tion, the wing is set at a slightly negative
      power, high wing loading, a conventional             account for much of the airframe's strength,      angle of incidence (minus one degree at the
      configuration and meticulous attention to            reducing the need for complex and heavy in-       root, minus four degrees at the tip) in order to
      drag reduction. That philosophy, and a dedi-         ternal structures. The wing has been static-      produce the least drag in cruise flight.
      cation to the highest standards of construc-         load tested to six Gs. Stress analysis calcula-      Rush rivets are used throughout the air-
      tion, are reflected in every inch of the SX300.      tions indicate that the failure point is beyond   frame. Communications and navigation an-
          The 300-horsepower Lycoming 10-540               nine Gs. Wing leading edges are fabricated as     tennas are buried in the fiberglass wing tips
      that powers the SX300 is one of the largest          single U-shaped sections, spanning from           and in the tail. The gear is operated by means
      horizontally opposed piston engines found            wing root to wing tip and curving aft to the      of an electrically actuated hydraulic system
      on general aviation singles; it is bolted to one
      of the smallest airframes. Wingspan is 10 feet
      less than a Piper Tomahawk's, and length is
      one foot shorter. The SX300's power to
      weight ratio of eight pounds per horsepower
      places the airplane in a class with some turbo-
      props, and so does its performance.
          Best initial rate of climb is 2,400 feet per
      minute at 125 knots. A cruise climb speed of
       160 knots yields about 1,000 fpm below
       10,000 feet. Cruise speed at 65-percent power
      and 12,500 feet is 231 knots, and range is 980
      nautical miles with a 45-minute reserve.
          Maneuvering speed in the SX300 is a high
      207 KIAS, which allows the pilot to descend
      without having to make substantial speed re-
      ductions. It also allows the pilot to maintain a
      relatively high speed in turbulence. The day I
      flew Swearingen's prototype, the tiny air-
      plane was hardly budged by strong midday
      Texas thermals, a consequence of its high
      33.6-pounds-per-square-foot wing loading.
          Trade-offs for the SX300's impressive top-
      end performance figures come in the form of
      high (for a single) approach and stall speeds.
      Recommended final approach speed is 100

62·    AUGUST 1986
  and is fully enclosed when retracted. The            through the cylinder heads more efficiently.            The airplane's aerobatic capability will
  flaps are hydraulically actuated.                       Several other modifications have been             tempt pilots. But a high degree of aerobatic
     Minimizing cooling drag while providing           made to the SX300 since initial flight testing.      proficiency will be required to avoid exces-
  even cooling to all cylinders was a significant      The horizontal tail area was increased ap-           sive speed build-up or inadvertent spins. At
  design objective. At the SX300's cruise              proximately 20 percent to improve low-speed          the moment, the airplane's spin characteris-
  speeds, intake air can actually "dam up" at          pitch control. Rudder chord was increased            tics are unknown. Swearingen says spin tests
  the cooling air inlets, adding substantial drag.     two inches to provide more control in a full-        will be conducted in the future, after the air-
  The solution was to modify the prototype's           power stall. Positive servo tabs were added to       plane has been rigged with a spin recovery
  original cowling by extending the cooling air        the ailerons to reduce roll forces, and an anti-     parachute and a canopy jettison system.
  inlets forward almost to the prop. The origi-        servo tab was added to the elevator to in-              The stall break may seem rather sharp to
  nal nearly rectangular inlet shape was re-           crease pitch forces. Wing dihedral was in-           pilots accustomed to the stall characteristics
  jected in favor of a rounded inlet, and the          creased from three to four degrees to improve        of factory-built high-performance singles.
  inlet leading edges were molded in an airfoil        roll stability.                                      Overzealous application of the SX300's sensi-
  shape. Felt seals surround the propeller shaft           Inside the cockpit, the prototype's soft         tive controls could lead the pilot to exacerbate
  to prevent cooling air from reversing course          leather upholstery adds an appropriate touch        the stall. Again, pilot proficiency will be the
  and flowing back out the front of the cowl.           of luxury to such an exotic airplane. But the       key to safe stall recovery.
  The upper half of the powerplant is tightly           important inside story has to do with                   Swearingen Aircraft has shipped three of
  baffled in order to direct cooling air down           Swearingen's attempt to provide substantial          the aircraft's six subassembly kits to build-
                                                        system redundancy. The pilot's gyro instru-          ers-those for the empennage, wings and fu-
                                                        ments are electrically driven, while the co-         selage. Shipments of the engine installation
                                                        pilot's gyros are air-driven. Neither an electri-    and landing gear kits are scheduled to com-
                                                        cal failure nor a vacuum failure will leave the      mence in September 1986. The cockpit com-
                                                        pilot without attitude and direction reference.      pletion kit will be the last to be shipped. Kits
                                                          A split-bus electrical system allows the pi-       have been shipped to 88 individuals, 69 of
                                                       lot to quickly shed electrical load while re-         whom are actively building airplanes, accord-
                                                       taining essential items-the pilot's turn co-          ing to Swearingen.
                                                       ordinator, one navcom, the fuel boost pump              SX300 builders interviewed for this article
    lllllovatioll   alld attelltioll   to detail are   and a map light. The prototype also is               praise the quality of materials and prefab-
      reflected ill the distillctive  shape of a       equipped with a two-axis S-Tee autopilot             ricated parts. Drawings and assembly instruc-
Ilaturallami/Jar     flow airfoil alld the 5X300's     specially programmed for the pitch and roll          tions for the airplane are first-rate, and tech-
        roullded, airfoil-shaped     air illiets.      characteristics of the SX300.                        nical support from Swearingen Aircraft has
                                                          Flying characteristics are sophisticated,         been good, they say. But some also say that
                                                       also. Prospective pilots need training in truly      the SX300 is as complex and demanding a
                                                       high-performance aircraft; transition training       building project as one is likely to find among
                                                       tailored to the SX300 would be even better. It       kit aircraft.
                                                       is not an aircraft that should be treated lightly       Swearingen will not estimate building time
                                                       in allY aspect of its operation.                     for the SX300 because, he says, it will vary
                                                          Even with the addition of the anti-servo          considerably with the experience of the
                                                       tab, pitch forces are quite light in all phases of   builder. One spare-time builder, who expects
                                                       flight. Aileron and rudder forces are as nicely      to take at least five years to finish his airplane,
                                                       balanced as they are responsive. Roll rate is        quips that "The SX300 is for the buyer who
                                                       140 degrees per second, and aileron rolls are        wants a fast airplane, but doesn't need an
                                                       nearly effortless.                                   airplane fast." Some purchasers have hired
                                                                                                            experienced aircraft mechanics or home-
                                                                                                            builders to work full-time on the construction
                                                                                                            of their SX300s.
                                                                                                               Building time may be reduced substan-
                                                                                                            tially, however, if Swearingen wins FAA ap-
                                                                                                            proval for his plan to offer what he refers to as
                                                                                                            the SX300 "big chunk" kit. This kit would
                                                                                                            provide a fully assembled fuselage, com-
                                                                                                            pleted wings, and an empennage complete
                                                                                                            except for the left-hand stabilizer-the only
                                                                                                            component that will have to be fashioned out
                                                                                                            of sheet metal. Rather than spending hun-
                                                                                                            dreds of hours drilling holes and driving riv-
                                                                                                            ets, the builder will bolt the airframe together
                                                                                                            and install the various aircraft systems.
                                                                                                               The kit still will meet the amateur-built re-
                                                                                                            quirements, Swearingen says, because the
                                                                                                            homebuilder still puts in more than half the
                                                                                                            hours of labor necessary to complete the air-
                                                                                                            plane, while learning just as much about air-
                                                                                                            craft construction as with the previous kit.
                                                                                                            (FAA regulations require that amateur-built
                                                                                                            airplanes be assembled solely for education
                                                                                                            or recreation.) A price has not yet been ar-
                                                                                                            rived at for the new kit, but it too will be a big
                                                                                                            chunk, says Swearingen. -J. Jeffersoll Miller

                                                                                                                                                   AOPA PILOT • 63

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